Boost.Container aims for full C++11 conformance
except reasoned deviations, backporting as much as possible for C++03. Obviously,
this conformance is a work in progress so this section explains what C++11
features are implemented and which of them have been backported to C++03 compilers.

For compilers with rvalue references and for those C++03 types that use
Boost.Move rvalue reference
emulation Boost.Container supports all C++11
features related to move semantics: containers are movable, requirements
for value_type are those
specified for C++11 containers.

For compilers with variadic templates, Boost.Container
supports placement insertion (emplace,
...) functions from C++11. For those compilers without variadic templates
support Boost.Container uses the preprocessor
to create a set of overloads up to a finite number of parameters.

C++03 was not stateful-allocator friendly. For compactness of container objects
and for simplicity, it did not require containers to support allocators with
state: Allocator objects need not be stored in container objects. It was
not possible to store an allocator with state, say an allocator that holds
a pointer to an arena from which to allocate. C++03 allowed implementors
to suppose two allocators of the same type always compare equal (that means
that memory allocated by one allocator object could be deallocated by another
instance of the same type) and allocators were not swapped when the container
was swapped.

C++11 further improves stateful allocator support through std::allocator_traits.
std::allocator_traits is the protocol between
a container and an allocator, and an allocator writer can customize its behaviour
(should the container propagate it in move constructor, swap, etc.?) following
allocator_traits requirements.
Boost.Container not only supports this model
with C++11 but also backports it to C++03
via boost::container::allocator_traits
including some C++17 changes. This class offers some workarounds for C++03
compilers to achieve the same allocator guarantees as std::allocator_traits.

In [Boost.Container] containers, if possible, a single allocator is hold
to construct value_types.
If the container needs an auxiliary allocator (e.g. an array allocator used
by deque or stable_vector), that allocator is also
stored in the container and initialized from the user-supplied allocator
when the container is constructed (i.e. it's not constructed on the fly when
auxiliary memory is needed).

C++11 improves stateful allocators with the introduction of std::scoped_allocator_adaptor
class template. scoped_allocator_adaptor
is instantiated with one outer allocator and zero or more inner allocators.

A scoped allocator is a mechanism to automatically propagate the state of
the allocator to the subobjects of a container in a controlled way. If instantiated
with only one allocator type, the inner allocator becomes the scoped_allocator_adaptor itself, thus using
the same allocator resource for the container and every element within the
container and, if the elements themselves are containers, each of their elements
recursively. If instantiated with more than one allocator, the first allocator
is the outer allocator for use by the container, the second allocator is
passed to the constructors of the container's elements, and, if the elements
themselves are containers, the third allocator is passed to the elements'
elements, and so on.

Boost.Container implements its own scoped_allocator_adaptor
class and backports this feature also to C++03 compilers.
Due to C++03 limitations, in those compilers the allocator propagation implemented
by scoped_allocator_adaptor::construct
functions will be based on traits (constructible_with_allocator_suffix
and constructible_with_allocator_prefix)
proposed in N2554:
The Scoped Allocator Model (Rev 2) proposal. In conforming C++11
compilers or compilers supporting SFINAE expressions (when BOOST_NO_SFINAE_EXPR is NOT defined), traits
are ignored and C++11 rules (is_constructible<T,Args...,inner_allocator_type>::value and is_constructible<T,allocator_arg_t,inner_allocator_type,Args...>::value) will be used to detect if the allocator
must be propagated with suffix or prefix allocator arguments.

Boost.Container implements C++14
Null Forward Iterators, which means that value-initialized iterators
may be compared and compare equal to other value-initialized iterators of
the same type. Value initialized iterators behave as if they refer past the
end of the same empty sequence (example taken from N3644):

vector does not support
the strong exception guarantees given by std::vector
in functions like insert,
push_back, emplace, emplace_back,
resize, reserve
or shrink_to_fit for either
copyable or no-throw moveable classes. In C++11 move_if_noexcept
is used to maintain C++03 exception safety guarantees combined with C++11
move semantics. This strong exception guarantee degrades the insertion performance
of copyable and throwing-moveable types, degrading moves to copies when such
types are inserted in the vector using the aforementioned members.

This strong exception guarantee also precludes the possibility of using some
type of in-place reallocations that can further improve the insertion performance
of vector See Extended
Allocators to know more about these optimizations.

vector always uses
move constructors/assignments to rearrange elements in the vector and uses
memory expansion mechanisms if the allocator supports them, while offering
only basic safety guarantees. It trades off exception guarantees for an improved
performance.

//Given std::vector<int> vv.insert(v.begin(),v[2]);//v[2] can be changed by moving elements of vector//Given std::list<int> l:l.remove(*l.begin())//The operation could delete the first element, and then continue trying to access it.

The adopted resolution, NAD (Not A Defect), implies that previous operations
must be well-defined. This requires code to detect a reference to an inserted
element and an additional copy in that case, impacting performance even when
references to already inserted objects are not used. Note that equivalent
functions taking rvalue references or iterator ranges require elements not
already inserted in the container.

Boost.Container prioritizes performance
and has not implemented the NAD resolution: in functions that might modify
the argument, the library requires references to elements not stored in the
container. Using references to inserted elements yields to undefined behaviour
(although in debug mode, this precondition violation could be notified via
BOOST_ASSERT).

vector<bool> specialization
has been quite problematic, and there have been several unsuccessful tries
to deprecate or remove it from the standard. Boost.Container
does not implement it as there is a superior Boost.DynamicBitset
solution. For issues with vector<bool>
see the following papers:

“But it is a shame that the C++ committee gave this excellent
data structure the name vector<bool> and that it gives no guidance
nor encouragement on the critical generic algorithms that need to be
optimized for this data structure. Consequently, few std::lib implementations
go to this trouble.”

“In 1998, admitting that the committee made a mistake
was controversial. Since then Java has had to deprecate such significant
portions of their libraries that the idea C++ would be ridiculed for
deprecating a single minor template specialization seems quaint.”

“vector<bool> is not a container and vector<bool>::iterator is not a random-access iterator
(or even a forward or bidirectional iterator either, for that matter).
This has already broken user code in the field in mysterious ways.”

“vector<bool> forces a specific (and potentially
bad) optimization choice on all users by enshrining it in the standard.
The optimization is premature; different users have different requirements.
This too has already hurt users who have been forced to implement workarounds
to disable the 'optimization' (e.g., by using a vector<char> and
manually casting to/from bool).”

So boost::container::vector<bool>::iterator returns real bool
references and works as a fully compliant container. If you need a memory
optimized version of boost::container::vector<bool>,
please use Boost.DynamicBitset.

Boost.Container uses std::memset
with a zero value to initialize some types as in most platforms this initialization
yields to the desired value initialization with improved performance.

Following the C11 standard, Boost.Container
assumes that for any integer type, the object representation where
all the bits are zero shall be a representation of the value zero in that
type. Since _Bool/wchar_t/char16_t/char32_t are also integer types in C, it considers
all C++ integral types as initializable via std::memset.

By default, Boost.Container also considers
floating point types to be initializable using std::memset.
Most platforms are compatible with this initialization, but in case this
initialization is not desirable the user can #defineBOOST_CONTAINER_MEMZEROED_FLOATING_POINT_IS_NOT_ZERO
before including library headers.

By default, it also considers pointer types (pointer and pointer to function
types, excluding member object and member function pointers) to be initializable
using std::memset. Most platforms are compatible with
this initialization, but in case this initialization is not desired the user
can #defineBOOST_CONTAINER_MEMZEROED_POINTER_IS_NOT_ZERO
before including library headers.